The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from an engine to a transmission or in a transfer case of a four-wheel-drive vehicle.
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from the engine to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures. Examples of silent chain is found in U.S. Pat. No. 4,342,560 and U.S. Pat. No. 4,832,668, which are both incorporated herein by reference.
Conventional silent chains typically include both guide links and driving links. The guide links are positioned on the outside edges of alternate sets of links. The guide links typically act to position the silent chain laterally on the sprocket. Guide links in silent chains typically do not mesh with the sprocket.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and the sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are typically designed so that at least some of the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links, or driving links, contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the flanks and the sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental contact, or can include root contact or side contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Movement of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket may be mounted on the engine crankshaft and the driven sprocket mounted on a valve camshaft. A silent chain for an engine timing drive application is shown in U.S. Pat. No. 4,758,210, which is incorporated herein by reference. Various types of engine timing systems and configurations are also shown in U.S. application Ser. No. 08/131,473, filed Oct. 4, 1993, pending which is incorporated herein by reference.
Noise is associated with such chain drives. Noise is generated by a variety of sources, but in silent chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket.
The meshing impact sound is generally a periodic sound in chain drives. The impact sound is repeated with a frequency approximately equal to that of the frequency of the chain meshing with the sprocket. The frequency can be related to the number of teeth on the sprocket and the speed of the sprocket. The impacts can produce sound having objectionable pure sonic tones.
Another cause of noise is the chordal action of the sprockets as the chain is driven about the sprockets. Chordal action occurs as the chain link enters the sprocket from the free chain. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free chain or span (the part of the chain between the sprockets) in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets. This vibratory movement can also produce a pure sonic tone at the frequency of the chain mesh frequency or a derivative of it.
Many efforts have been made to decrease the noise level and pitch frequency distribution in chain drives of the silent chain variety to minimize the objectionable effects of the pure sonic tones. The problem of noise reduction in silent chain drives was addressed in U.S. Pat. No. 4,342,560 by changing the contacts between the link flanks of a silent chain and the sprockets by having differently configured link flanks in different sets of the chain. By mixing links of differing flank configuration, U.S. Pat. No. 4,342,560 attempted to modify the pattern of sound emanating from the chain contacting the sprocket by altering the types of link configurations and thus altering the point and rhythm of contacts.
U.S. Pat. No. 4,915,675, which is incorporated herein by reference, utilized the same concept of modifying the pattern of sound emanating from the chain by altering the types of link configurations. The patent teaches the utilization of an asymmetrically shaped link form which is then oriented in two different directions in the chain assembly to alter the point and rhythm of chain to sprocket contacts.
Other attempts to alter the rhythm of contacts between the silent chain drive and the sprocket have focused on the modification of the sprocket teeth. For example, U.S. Pat. No. 3,377,875 and U.S. Pat. No. 3,495,468, teach relief of the sprocket teeth, or even elimination of sprocket teeth, in order to achieve noise reduction in contacts between the links of the silent chain and the sprocket teeth.
A belt for a cone pulley transmission is described in U.S. Pat. No. 4,344,761, which is designed to prevent sympathetic vibrations between the belt and the cone pulleys. The disclosed belt construction includes segmented steel belts with multiple segments that do not positively engage a sprocket. The patent teaches causing the lengths of selected links between associated articulation points to differ from those of the remaining links. The links of U.S. Pat. No. 4,344,761 are not designed to engage sprocket teeth and thus are not subject to any of the constraints of inverted tooth links. U.S. Pat. No. 4,650,445 discusses various other methods of construction of silent chains and chain-belts for variable pulley transmissions that are attempts to modify the generated noise pattern.
The present invention utilizes these generic concepts of noise reduction in an inverted tooth or silent chain. The present invention seeks to provide a silent chain construction that modifies the pattern of chain and sprocket contacts through the use of variable pitches or unequal pitch lengths in the chain. These unequal pitch lengths are achieved through the use of unequal pin separation distances as well as unequal aperture separation distances, which will result in variation of the pitches of the links of the chain. The pitch lengths are varied or randomized through the length of the chain to modify the chain link and sprocket contacts. The randomization of the pitch length may also be utilized in combination with randomization of the link flank contours or profiles. The randomization of pitch lengths with randomization of link flank contours provides an additional element of randomization or modification of the pattern of chain and sprocket contacts.
The present invention also has application in the design of a chain for a specific sprocket center distance. Unlike chains in which all links are formed of identical pitch, the chain of the present invention can insert links of different pitch lengths to accommodate a special sprocket-to-sprocket center distance. By controlling the number of pitches and links, and using two or more pitches in the chain, the chain may accommodate a variable center distance. Such a chain has application outside of the area of use of variable pitch for noise reduction.
Prior art chain assemblies have utilized pins of various configurations and placement in a variety of locations. However, those assemblies have provided placement of the pins in locations in the links in order to achieve uniform spacing for proper engagement with the sprockets. For example, U.S. Pat. No. 1,868,334 discloses a chain in which the centers of articulation are longer or shorter in different parts of the chain. The patent describes a chain in which all of the links are of identical configuration and orientation and the center of curvatures of the pins are eccentric or offset from the joint so that in some joints the centers are forward of the joint and in some joints the centers are backward of the joint. The patent does not teach variation of pitch lengths where the pins are identical or where the centers of articulation are not located on opposite sides of the links.